Here: http://dlang.org/operatoroverloading.html#FunctionCall
is this example:
----
import std.stdio;

struct F {
	int opCall() {
		return 0;
	}
	
	int opCall(int x, int y, int z) {
		return x * y * z;
	}
}

void main() {
	F f;
	int i;

	i = f();      // same as i = f.opCall();
	i = f(3,4,5); // same as i = f.opCall(3,4,5);
}
----

And it works of course. But what if I want to templatize opCall? How can I call it?

----
import std.stdio;

struct F {
	T opCall(T = int)(int a, int b, int c) {
		return cast(T)(a * b * c);
	}
}

void main() {
	F f;
	int i = f(3,4,5);
	float f_ = f!float(6, 7, 8);
}
----

Does not work, it fails with:
Error: template instance f!float f is not a template declaration, it is a variable

> void main() {
> 	F f;
> 	int i = f(3,4,5);
> 	float f_ = f!float(6, 7, 8);
> }
> ----
>
> Does not work, it fails with:
> Error: template instance f!float f is not a template declaration, it is a variable

f.opCall!float(6, 7, 8);

On Thursday, 30 January 2014 at 16:24:00 UTC, Stanislav Blinov wrote:
>> void main() {
>> 	F f;
>> 	int i = f(3,4,5);
>> 	float f_ = f!float(6, 7, 8);
>> }
>> ----
>>
>> Does not work, it fails with:
>> Error: template instance f!float f is not a template declaration, it is a variable
>
> f.opCall!float(6, 7, 8);

... Yes, of course. But where is the sense to use opCall if I need to call it explicitly?

On Thursday, 30 January 2014 at 16:28:42 UTC, Namespace wrote:
> On Thursday, 30 January 2014 at 16:24:00 UTC, Stanislav Blinov wrote:
>>> void main() {
>>> 	F f;
>>> 	int i = f(3,4,5);
>>> 	float f_ = f!float(6, 7, 8);
>>> }
>>> ----
>>>
>>> Does not work, it fails with:
>>> Error: template instance f!float f is not a template declaration, it is a variable
>>
>> f.opCall!float(6, 7, 8);
>
> ... Yes, of course. But where is the sense to use opCall if I need to call it explicitly?

Could you not use opDispatch? Not sure if you can templatize it
or not though...

On Thursday, 30 January 2014 at 16:47:46 UTC, Frustrated wrote:
> On Thursday, 30 January 2014 at 16:28:42 UTC, Namespace wrote:
>> On Thursday, 30 January 2014 at 16:24:00 UTC, Stanislav Blinov wrote:
>>>> void main() {
>>>> 	F f;
>>>> 	int i = f(3,4,5);
>>>> 	float f_ = f!float(6, 7, 8);
>>>> }
>>>> ----
>>>>
>>>> Does not work, it fails with:
>>>> Error: template instance f!float f is not a template declaration, it is a variable
>>>
>>> f.opCall!float(6, 7, 8);
>>
>> ... Yes, of course. But where is the sense to use opCall if I need to call it explicitly?
>
> Could you not use opDispatch? Not sure if you can templatize it
> or not though...

Example? I did not know how.

On Thursday, 30 January 2014 at 15:59:28 UTC, Namespace wrote:
> Here: http://dlang.org/operatoroverloading.html#FunctionCall
> is this example:
> ----
> import std.stdio;
>
> struct F {
> 	int opCall() {
> 		return 0;
> 	}
> 	
> 	int opCall(int x, int y, int z) {
> 		return x * y * z;
> 	}
> }
>
> void main() {
> 	F f;
> 	int i;
>
> 	i = f();      // same as i = f.opCall();
> 	i = f(3,4,5); // same as i = f.opCall(3,4,5);
> }
> ----
>
> And it works of course. But what if I want to templatize opCall? How can I call it?
>
> ----
> import std.stdio;
>
> struct F {
> 	T opCall(T = int)(int a, int b, int c) {
> 		return cast(T)(a * b * c);
> 	}
> }
>
> void main() {
> 	F f;
> 	int i = f(3,4,5);
> 	float f_ = f!float(6, 7, 8);
> }
> ----
>
> Does not work, it fails with:
> Error: template instance f!float f is not a template declaration, it is a variable

This is probably a bug. You should file it in Bugzilla.

On Thursday, 30 January 2014 at 16:53:33 UTC, Namespace wrote:
> On Thursday, 30 January 2014 at 16:47:46 UTC, Frustrated wrote:
>> On Thursday, 30 January 2014 at 16:28:42 UTC, Namespace wrote:
>>> On Thursday, 30 January 2014 at 16:24:00 UTC, Stanislav Blinov wrote:
>>>>> void main() {
>>>>> 	F f;
>>>>> 	int i = f(3,4,5);
>>>>> 	float f_ = f!float(6, 7, 8);
>>>>> }
>>>>> ----
>>>>>
>>>>> Does not work, it fails with:
>>>>> Error: template instance f!float f is not a template declaration, it is a variable
>>>>
>>>> f.opCall!float(6, 7, 8);
>>>
>>> ... Yes, of course. But where is the sense to use opCall if I need to call it explicitly?
>>
>> Could you not use opDispatch? Not sure if you can templatize it
>> or not though...
>
> Example? I did not know how.


doesn't seem to work with templates, I suppose you could try and
add it as a feature request?

module main;

import std.stdio;

interface A
{
	void foo();
	static final New() { }
}

class B : A
{
	void foo() { writeln("this is B.foo"); }

	void opDispatch(string s, T)(int i) {
		writefln("C.opDispatch('%s', %s)", s, i);
	}

}


void main() {
	B a = new B;
	//a.foo();

	a.test!int(3); // any *good* reason why this shouldn't work?

}

Also,

http://dlang.org/operatoroverloading.html#Dispatch

and possible solution to your problem:

http://www.digitalmars.com/d/archives/digitalmars/D/opDispatch_and_template_parameters_117095.html

Couldn't get code to compile though... but if it did, it should
solve your problem.

On Thursday, 30 January 2014 at 16:55:01 UTC, Meta wrote:
> On Thursday, 30 January 2014 at 15:59:28 UTC, Namespace wrote:
>> Here: http://dlang.org/operatoroverloading.html#FunctionCall
>> is this example:
>> ----
>> import std.stdio;
>>
>> struct F {
>> 	int opCall() {
>> 		return 0;
>> 	}
>> 	
>> 	int opCall(int x, int y, int z) {
>> 		return x * y * z;
>> 	}
>> }
>>
>> void main() {
>> 	F f;
>> 	int i;
>>
>> 	i = f();      // same as i = f.opCall();
>> 	i = f(3,4,5); // same as i = f.opCall(3,4,5);
>> }
>> ----
>>
>> And it works of course. But what if I want to templatize opCall? How can I call it?
>>
>> ----
>> import std.stdio;
>>
>> struct F {
>> 	T opCall(T = int)(int a, int b, int c) {
>> 		return cast(T)(a * b * c);
>> 	}
>> }
>>
>> void main() {
>> 	F f;
>> 	int i = f(3,4,5);
>> 	float f_ = f!float(6, 7, 8);
>> }
>> ----
>>
>> Does not work, it fails with:
>> Error: template instance f!float f is not a template declaration, it is a variable
>
> This is probably a bug. You should file it in Bugzilla.

Ok, done:
https://d.puremagic.com/issues/show_bug.cgi?id=12043

On Thursday, 30 January 2014 at 17:46:19 UTC, Frustrated wrote:
> Also,
>
> http://dlang.org/operatoroverloading.html#Dispatch
>
> and possible solution to your problem:
>
> http://www.digitalmars.com/d/archives/digitalmars/D/opDispatch_and_template_parameters_117095.html
>
> Couldn't get code to compile though... but if it did, it should
> solve your problem.

opDispatch is called if you try to call a non existing member. But in this case you don't call a member. ;)